A variety of energy sources are presently available, such as nuclear, solar, hydroelectric, geothermal, wind and tidal power. However, by far the most common and convenient sources of energy at present are those based on the combustion of carbonaceous products. For example, coal, gas, coke, wood, petroleum and diesel. By necessity, when such carbonaceous products burn they produce oxides of carbon, most notably CO2.
CO2 has become notorious as a “greenhouse” gas and the 1997 Kyoto protocol aims to reduce the level of such greenhouse gases and ultimately minimise the extent of global warming and its consequences.
The use of Hydrogen as a fuel represents an attractive alternative.
Fuel cells convert hydrogen directly into electrical energy by reactions which involve the reforming of hydrogen rich organic compounds (such as methane and methanol) by means of steam, catalysis, elevated temperatures and the like. Fuel cells operate by the direct conversion of chemical energy in a fuel to electrical energy without an intermediate combustion change. They represent the principal next generation source of mass energy production and are poised to make a significant contribution to power generation. However, these fuel cells suffer from the disadvantage that they all produce oxides of carbon, such as CO or CO2, when using reformed organics as their hydrogen source.
On the earth, free or uncombined hydrogen is rare. It is commonly found in a combined form such as water, hydrocarbons and all plant and animal matter. In producing elemental hydrogen, the primary considerations are usually cost and convenience. In the laboratory, pure hydrogen is usually made by the reaction of a suitable metal with a displacement acid or by the electrolysis of water. For commercial hydrogen the primary sources are water and hydrocarbons. These endothermic processes require energy.
Molecular hydrogen is an important source of energy, as evidenced by the endothermic nature of its production. Its internal energy can be released either by combustion or by reaction with oxygen in a fuel cell.
However, the combustion of hydrogen gas directly produces no oxides of carbon-clean combustion produces theoretically only pure water.
The electronic and dehydrogenation process mentioned above for the production of molecular hydrogen produce by-products which may be unwanted. Electrolysis produces oxygen, which is useful, but dehydrogenation of organic compounds produces carbon dioxide, a global warming gas. These processes also require considerable energy input from external sources.
Attempts have been made to produce pure molecular hydrogen by self sustaining exothermic reactions. Conventional hydrogen generators are described in U.S. Pat. No. 4,463,063 and refer to the reaction of metal hydrides with water and the use of extruded electropositive metal anodes which gradually dissolve in the electrolytes, to provide electrons for discharge at inert cathodes.
In all of these instances the resulting compounds apart from the hydrogen produced, are regarded as waste, with problems associated with their collection and disposal.
Pure hydrogen can be liberated from water according to the following half cell equation:2H2O+2e−→20H−+H2 E0=−0.828.
In theory, any electropositive system with an E0 value greater than 0.828 V can react with water to produce hydrogen. Examples of such electropositive systems with E0 values above 0.828 V include hydrides, for example:2H−→H2+2e− E0=2.23 V
Although reactions of metals to produce hydrogen such as that given by:Al+H2O+NaOH→NaAlO2+1½H2are chemically feasible, they are kinetically very slow and the hydrogen is produced at a slow rate over a long period. This “trickle” of hydrogen is unsatisfactory for commercial use.
It is desirable therefore to maximise not only the amount of hydrogen produced by a cell, but also the speed of hydrogen production.
More recent inventions in the field disclose generators for the production of hydrogen from methanol (U.S. Pat. Nos. 5,172,052 and 5,885,727). However, a by-product of the said reaction is carbon monoxide which is adsorbed by the catalyst, causing “catalyst poisoning”, which refers to the deterioration of the catalytic function of the electrode, and subsequent lowering in the energy efficiency of the system. In order to minimise this problem, such generators must necessarily be equipped with means for measuring the carbon monoxide concentration in the system as well as means for decreasing it.
Other recent inventions in this field concentrate on the delivery of the reagents into the cell (eg U.S. Pat. No. 5,817,157, U.S. Pat. No. 5,514,353). It will be understood that the above citations are not indicative of the state of the common general knowledge.
The transport and storage of energy and fuel are also often problematic. The direct transference of electricity results in substantial losses of energy when the electricity is transmitted over long distances. Large infrastructure investments are also required for electricity transmittal over long distances which require the use of high tension wires and towers and booster and substation arrays to ensure delivery of adequate power to the consumer.
The transmission of gaseous fuels, such as natural gas, also requires substantial infrastructure to ensure adequate pressure and supply to consumers. Single use and rechargeable cylinders are practicable in some cases but even household size cylinders are bulky and heavy and require regular replacement.
It is an object of the present invention to overcome or ameliorate at least one of the disadvantages of the prior art, or to provide a useful alternative.
The energy generator produces pure gaseous hydrogen by the reduction of water by electro positive half-cell reactions involving two or more electropositive redox systems. The systems are chosen to maximise hydrogen production and desirably to produce by-products which are valuable rather than harmful or useless.